78 ideas
| 21422 | Moral self-knowledge is the beginning of all human wisdom [Kant] |
| 21408 | For any subject, its system of non-experiential concepts needs a metaphysics [Kant] |
| 21416 | Philosophers should not offer multiple proofs - suggesting the weakness of each of them [Kant] |
| 13689 | 'Theorems' are formulas provable from no premises at all [Sider] |
| 13705 | Truth tables assume truth functionality, and are just pictures of truth functions [Sider] |
| 13706 | Intuitively, deontic accessibility seems not to be reflexive, but to be serial [Sider] |
| 13710 | In D we add that 'what is necessary is possible'; then tautologies are possible, and contradictions not necessary [Sider] |
| 13711 | System B introduces iterated modalities [Sider] |
| 13708 | S5 is the strongest system, since it has the most valid formulas, because it is easy to be S5-valid [Sider] |
| 13712 | Epistemic accessibility is reflexive, and allows positive and negative introspection (KK and K¬K) [Sider] |
| 13714 | We can treat modal worlds as different times [Sider] |
| 13720 | Converse Barcan Formula: □∀αφ→∀α□φ [Sider] |
| 13718 | The Barcan Formula ∀x□Fx→□∀xFx may be a defect in modal logic [Sider] |
| 13723 | System B is needed to prove the Barcan Formula [Sider] |
| 13715 | You can employ intuitionist logic without intuitionism about mathematics [Sider] |
| 13678 | The most popular account of logical consequence is the semantic or model-theoretic one [Sider] |
| 13679 | Maybe logical consequence is more a matter of provability than of truth-preservation [Sider] |
| 13682 | Maybe logical consequence is impossibility of the premises being true and the consequent false [Sider] |
| 13680 | Maybe logical consequence is a primitive notion [Sider] |
| 13722 | A 'theorem' is an axiom, or the last line of a legitimate proof [Sider] |
| 13696 | When a variable is 'free' of the quantifier, the result seems incapable of truth or falsity [Sider] |
| 13700 | A 'total' function must always produce an output for a given domain [Sider] |
| 13703 | λ can treat 'is cold and hungry' as a single predicate [Sider] |
| 13688 | Good axioms should be indisputable logical truths [Sider] |
| 13687 | No assumptions in axiomatic proofs, so no conditional proof or reductio [Sider] |
| 13690 | Proof by induction 'on the length of the formula' deconstructs a formula into its accepted atoms [Sider] |
| 13691 | Induction has a 'base case', then an 'inductive hypothesis', and then the 'inductive step' [Sider] |
| 13685 | Natural deduction helpfully allows reasoning with assumptions [Sider] |
| 13686 | We can build proofs just from conclusions, rather than from plain formulae [Sider] |
| 13697 | Valuations in PC assign truth values to formulas relative to variable assignments [Sider] |
| 13684 | The semantical notion of a logical truth is validity, being true in all interpretations [Sider] |
| 13704 | It is hard to say which are the logical truths in modal logic, especially for iterated modal operators [Sider] |
| 13724 | In model theory, first define truth, then validity as truth in all models, and consequence as truth-preservation [Sider] |
| 13698 | In a complete logic you can avoid axiomatic proofs, by using models to show consequences [Sider] |
| 13699 | Compactness surprisingly says that no contradictions can emerge when the set goes infinite [Sider] |
| 13701 | A single second-order sentence validates all of arithmetic - but this can't be proved axiomatically [Sider] |
| 13692 | A 'precisification' of a trivalent interpretation reduces it to a bivalent interpretation [Sider] |
| 13695 | Supervaluational logic is classical, except when it adds the 'Definitely' operator [Sider] |
| 13693 | A 'supervaluation' assigns further Ts and Fs, if they have been assigned in every precisification [Sider] |
| 13694 | We can 'sharpen' vague terms, and then define truth as true-on-all-sharpenings [Sider] |
| 13683 | A relation is a feature of multiple objects taken together [Sider] |
| 13702 | The identity of indiscernibles is necessarily true, if being a member of some set counts as a property [Sider] |
| 13721 | 'Strong' necessity in all possible worlds; 'weak' necessity in the worlds where the relevant objects exist [Sider] |
| 13707 | Maybe metaphysical accessibility is intransitive, if a world in which I am a frog is impossible [Sider] |
| 13709 | Logical truths must be necessary if anything is [Sider] |
| 21410 | That a concept is not self-contradictory does not make what it represents possible [Kant] |
| 13716 | 'If B hadn't shot L someone else would have' if false; 'If B didn't shoot L, someone else did' is true [Sider] |
| 13717 | Transworld identity is not a problem in de dicto sentences, which needn't identify an individual [Sider] |
| 13719 | Barcan Formula problem: there might have been a ghost, despite nothing existing which could be a ghost [Sider] |
| 21421 | Within nature man is unimportant, but as moral person he is above any price [Kant] |
| 21415 | Duty is impossible without prior moral feeling, conscience, love and self-respect [Kant] |
| 21409 | Moral principles do not involve feelings [Kant] |
| 21431 | The love of man is required in order to present the world as a beautiful and perfect moral whole [Kant] |
| 21437 | All morality directs the will to love of others' ends, and respect for others' rights [Kant] |
| 21429 | The duty of love is to makes the ends of others one's own [Kant] |
| 21411 | A duty of virtue is a duty which is also an end [Kant] |
| 21413 | Virtue is strong maxims for duty [Kant] |
| 21414 | The supreme principle of virtue is to find universal laws for ends [Kant] |
| 21436 | We are obliged to show the social virtues, but at least they make a virtuous disposition fashionable [Kant] |
| 21419 | If virtue becomes a habit, that is a loss of the freedom needed for adopting maxims [Kant] |
| 21417 | How do we distinguish a mean? The extremes can involve quite different maxims [Kant] |
| 21420 | If virtue is the mean between vices, then virtue is just the vanishing of vice [Kant] |
| 21418 | There is one principle of virtues; the virtues are distinguished by their objects [Kant] |
| 21425 | We can love without respect, and show respect without love [Kant] |
| 21427 | Respect is limiting our self-esteem by attending to the human dignity of other persons [Kant] |
| 21430 | Disrespect is using a person as a mere means to my own ends [Kant] |
| 21428 | Respect is purely negative (of not exalting oneself over others), and is thus a duty of Right [Kant] |
| 21426 | Love urges us to get closer to people, but respect to keep our distance [Kant] |
| 21434 | We must respect the humanity even in a vicious criminal [Kant] |
| 21412 | Humans are distinguished from animals by their capacity to set themselves any sort of end [Kant] |
| 21435 | Man is both social, and unsociable [Kant] |
| 20582 | World government needs a shared global identity [Oksala] |
| 20568 | The principles Rawls arrives at do not just conform to benevolence, but also result from choices [Oksala] |
| 20578 | Anarchists prefer local and communal government [Oksala] |
| 20574 | Utilitarianism neglects responsibility, duties and rights [Oksala] |
| 21433 | Violation of rights deserves punishment, which is vengeance, rather than restitution [Kant] |
| 21423 | Men can only have duties to those who qualify as persons [Kant] |
| 21424 | Cruelty to animals is bad because it dulls our empathy for pain in humans [Kant] |